CZ281902B6 - Process of continuous preparation of water-in-oil emulsion with a high internal proportion of emulsion phase, suitable for subsequent polymerization and dewatering under the formation of an absorption foamy material - Google Patents

Abstract

Disclosed is a process for the continuous preparation of high internal phase emulsions which are suitable for subsequent polymerization into polymeric foam materials that, upon dewatering, act as absorbents for aqueous body fluids. The process involves continuous introduction of a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is sufficient to thereby form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns. The formation of such a stable high internal phase emulsion is completed by feeding the contents of the dynamic mixing zone to and through a static mixing zone.

Description

(57)

The oil phase containing the monomers and the aqueous phase containing the electrolyte are continuously fed into the dynamic mixing zone with a relatively small ratio of the aqueous phase to the oil phase. The flow rates are then continuously adjusted to increase the ratio of the aqueous phase to the oil phase introduced into the dynamic mixing zone while subjecting the contents in the dynamic mixing zone to shear mixing sufficient to form an emulsion with a large internal phase aqueous phase which provides subsequent medium polymerization foam. 5 to 100 microns. The formation of such a stable emulsion with a large internal fraction of the aqueous phase is completed by introducing the content of the dynamic mixing zone into a static mixing zone. The foam material obtained is particularly suitable as a body fluid absorbent.

Process for the continuous preparation of a water-in-oil emulsion with a high internal fraction of the emulsion phase, suitable for subsequent polymerization and dewatering to form an absorbent foam material

Technical field

The invention relates to a process for the continuous preparation of a water-in-oil emulsion with a high internal fraction of the emulsion phase suitable for subsequent polymerization and dewatering to form absorbent foam material, such as warped but expandable absorbent foam material. Such High Intemal Phase Emulsion-HIPE emulsions contain certain types of monomer materials dissolved in the oil phase of the emulsion, so that especially suitable polymeric foam structures are formed when the emulsion is subjected to polymerization conditions. The specific emulsions prepared by the process of the invention provide polymerization of a foam structure which finds particular application as absorbents of body fluids. These foams are therefore suitable for use in 15 absorbent articles such as diapers and other incontinence articles.

BACKGROUND OF THE INVENTION

Emulsions with a relatively high proportion of the aqueous phase to the oil phase are known as HIPE (High Intemal Phase Emulsions). Methods for the continuous preparation of HIPE emulsions are described, for example, in U.S. Patent 3,558,717, issued February 23, 1971, to Bradley and Coke, and British Patent Publication No. 2194166, issued March 2, 1988.

HIPE emulsions containing polymerizable monomers in their external oil phase were prepared and were polymerized to study the geometric configurations of the oil and aqueous phases of such emulsions. For example, in Lissant and Mahan, A Study of Medium and High Intemal Phase Ratio Water / Polymer Emulsions Joumal of Colloid and Interface Science, Vol. 42, No. 1, January 1973, pages 201 to 208 disclose the preparation of water-in-oil emulsions containing 90% of the internal aqueous phase and using styrene monomer in the oil phase. Such emulsions are prepared by subjecting the combined water and oil phases to mixing and using an emulsifier and then polymerizing to a rigid porous structure with a cellular configuration, depending on the phase ratio of their emulsion precursors.

The preparation of HIPE emulsions suitable for polymerization into porous structures, for example foams suitable for absorbing and / or absorbing liquids, is also known. See, for example, U.S. Patent No. 4,773,910 to Barby et al., Issued January 10, 1989; U.S. Patent No. 4,612,334 to Jones et al. issued September 16, 1986, U.S. Pat. No. 4,606,958 to Haq et al.

of April 19, 1986 and U.S. Pat. No. 4,522,953 to Barby et al. of June 11, 1989, are always porous polymeric materials which can be prepared from HIPE emulsions and are suitable for releasing liquids such as hard surface cleaning solutions from products such as wipes and cleaning cloths.

It is also known in the art that the nature and properties of porous polymeric foam materials formed by polymerization of HIPE emulsions depend strongly on both the type of components that treat the polymerizable HIPE emulsions and the process conditions used to form the emulsion. For example, European Patent No. 60138, Unilever, September 15, 1982, describes a process for preparing absorbent porous polymers (e.g. foams) from HIPE emulsions consisting of at least 90% by weight of water in an oil phase containing polymerizable monomers, surfactants and polymerization. catalyst. U.S. Patent No. 4,788,225 to Edwards et al., Issued November 29, 1988, describes the preparation of porous polymeric materials whose flexibility is achieved by selecting certain types of monomers (styrene, alkyl (meta) crystals, crosslinking agents) and using certain operating conditions. to control cell size

Any porous polymer formed therefrom. In European Patent Publication No. EP-A-299762 z

On January 18, 1989, it is reported that the use of an electrolyte in the aqueous phase of polymerizable HIPE emulsions may affect the cell opening size of any porous polymeric foam material formed.

Although the existence and synthesis of polymerizable HIPE emulsions is known in the art, the preparation of HIPE emulsions suitable for polymerization into suitable absorbent foam materials is not a problem. Such HIPE emulsions, and in particular HIPE emulsions with a high aqueous phase to oil phase ratio, tend to be unstable. Very slight variations in monomer and crosslinking agent content in the emulsion, emulsifier choice, emulsion component concentration, and mixing temperature and / or mixing conditions may cause the emulsion to disintegrate or to at least some extent into separate aqueous and oil phases. While stable emulsions can be realized, variations in emulsion composition and operating conditions can significantly affect the properties and characteristics of any polymeric foam materials realized, thereby making such foam materials more or less useful for their intended use. Such difficulties in the preparation of HIPE emulsions can become more difficult when it is desired to produce polymerizable emulsions in a continuous process in industrial or pilot production to obtain commercially appropriate or developmental amounts of polymeric absorbent foam materials.

Taking into account these considerations, it is an object of the invention to provide a process for preparing certain types of HIPE emulsions that can be polymerized to foam materials especially suitable as absorbents of aqueous body fluids, i.e. foams suitable for absorbent articles such as diapers.

It is a further object of the present invention to provide a process for the preparation of HIPE emulsions that can be run continuously.

Yet another object of the invention is to provide a process for preparing HIPE emulsions that can be operated on a commercially significant scale.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention provides a process for the continuous preparation of a water-in-oil emulsion with a high internal phase emulsion phase suitable for subsequent polymerization and dewatering to form absorbent foam material such as warped but expandable absorbent foam material. The essence of this method according to the invention is that it is

A) a liquid oil phase stream consisting of i) from 3 to 41% of at least one water-insoluble styrene-based monomer, ii) from 27 to 73% of water-insoluble monofunctional rubbery comonomer selected from the group consisting of alkyl alkylates, alkyl methacrylates, allylacrylates, butadiene, substituted butadienes, vinylidene halides or combinations of such comonomers and comonomer types, iii) with a molar ratio of at least one water-insoluble styrene-based monomer to a monofunctional rubbery comonomic component in the oil phase ranging from 1:25 to 1.5: 1, iv) from 8 to 40 % water insoluble crosslinking agent; and

(v) from 2 to 33% of an oil-soluble emulsifier component, forming a stable water-in-oil emulsion; and

B) an aqueous phase stream consisting of an aqueous solution containing 0.2 to 40% by weight of a water-soluble electrolyte,

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(C) are simultaneously introduced into the dynamic mixing zone at flow rates at which the initial water to oil phase weight ratio is in the range of 2: 1 to 10: 1;

D) in the dynamic mixing zone, the combined streams are subjected to shear agitation at a rate of 1000 to 7000 s ^-1 to form an emulsified mixture and to maintain constant velocities of the oil and aqueous phase streams, then

E) the ratio of the aqueous phase to the oil phase fed to the dynamic mixing zone continuously increases in the range of 12: 1 to 100: 1 at an increasing rate of said ratio maintaining the emulsified nature of the content in the dynamic mixing zone and maintaining this content at 25 to 70 ° C while continuing to shear the emulsified content in the dynamic mixing zone at a rate of 100 to 7000 s ^-1 and forming an emulsion with a high internal fraction of the emulsion phase, providing subsequent polymerization of a foam with an average cell size of 5 to 100 microns,

F) continuously emulsifies the emulsified content from the dynamic mixing zone and introduces it to the static mixing zone, where it is further subjected to further shear mixing to form a completely stable emulsion with a high internal emulsion phase having a water phase to oil phase weight ratio of 12: 1 to 100: 1 then

G) The stable emulsion with a high internal fraction of the emulsion phase continuously withdraws from the static mixing zone and subsequently polymerizes and dewateres to a rigid absorbent foam.

In one preferred embodiment of the process according to the invention, the process is carried out as follows:

A) a liquid oil phase stream comprising by weight

(i) from 7 to 40% of at least one water-insoluble styrene-based monomer, (ii) from 27 to 66% water-insoluble monofunctional rubbery comonomer component, (iii) with a molar ratio of styrene-based monomer component to monofunctional rubbery comonomer component in the oil phase 1: 2 to 1: 1 iv) 10 to 25% water insoluble crosslinking agent and / or

v) from 4 to 25% of an emulsion component soluble in the oil phase, forming a stable water-in-oil emulsion 35;

(B) an aqueous phase stream consisting of an aqueous solution containing from 0.5 to 20% by weight of a water-soluble electrolyte;

(C) are simultaneously introduced into the dynamic mixing zone at flow rates at which the initial weight ratio of the aqueous phase to the oil phase is in the range of 2.5: 1 to 5: 1;

(D) the combined streams are subjected to shear mixing at a speed of 1500 to 3000 s v in the dynamic mixing zone

E) the ratio of the aqueous phase to the oil phase fed to the dynamic mixing zone is continuously increased in the range of 20: 1 to 70: 1 at a rate of increasing said ratio maintaining the emulsified nature of the content in the dynamic mixing zone and maintaining this content at 25 to 65 ° C, preferably 35 to 50 ° C, while continuing to shear the emulsified content in the dynamic mixing zone at a speed of 1500 to 3000 s ^-1 and forming an emulsion with a large internal fraction of the emulsion phase, providing subsequent polymerization with an average cell size of 10 to 90 micrometer, and then

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F) continuously emulsifies the emulsified content from the dynamic mixing zone and introduces it to the static mixing zone, where it is further subjected to further shear mixing to form a completely stable emulsion with a large internal emulsion phase having an aqueous phase to oil phase weight ratio of 20: 1 to 70: 1 .

In a further embodiment of the method according to the invention, it is used

(Ii) a water insoluble monofunctional rubbery comonomer component comprising comonomer types selected from the group consisting of butyl acrylate, 2-ethylhexylakiylate, butadiene, isoprene, or a combination of these comonomer types; diallyl phthalate, at least one polyacrylic diacrylate ester, or a combination of such difunctional monomer types,

v) an emulsifier component comprising an emulsifier selected from the group consisting of sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene fatty acid esters, and combinations of such emulsifiers;

(B) an aqueous solution comprising a water-soluble electrolyte composed of at least one water-soluble alkali metal or alkaline earth metal salt; and

E) Shear mixing is continued by means of a pin impeller to produce a foam having an average cell size in the range of 5 to 30 microns.

In another embodiment of the invention it is used

(A) (iv) divinylbenzene as a difunctional monomer; and

v) an emulsifier component comprising sorbitan monooleate and sorbitan trioleate at a weight ratio of monooleate to trioleate in the range of 2: 1 to 5: 1, or sorbitan monolaurate and a co-emulsifier in a weight ratio of monolaurate to co-emulsifier in the range of 1: 1 to 10: 1;

B) calcium chloride as a water-soluble electrolyte.

It is preferred that it is used

B) a water-soluble electrolyte further comprising 0.02 to 0.4% by weight of a water-soluble free radical polymerization initiator, particularly preferably 0.1 to 0.2% of an initiator.

In a further embodiment of the invention, the aqueous phase stream is first fed into the pilot-type dynamic mixing zone at a rate of 0.04 to 2.0 liters / minute and the oil phase stream at a rate of 0.02 to 0.2 liters / minute.

When using a commercial production type dynamic mixing device, the aqueous phase stream is first fed to the dynamic mixing zone at a rate of 25 to 250 liters / minute and the oil phase stream at a rate of 10 to 25 liters / minute.

After increasing the ratio of the aqueous phase to the oil phase, the effluent from the dynamic mixing zone is withdrawn at a pilot plant at a rate of 0.8 to 2.2 liters / minute and at a commercial production plant at a rate of 35 to 800 liters / minute.

The stable, high internal phase emulsion obtained by the process of the present invention, withdrawn from the static mixing zone, is then subjected to the conditions under which the

The polymerization of the polymerizable monomers, comonomers and crosslinkers in the oil phase of said high internal phase stable emulsion is followed by dewatering to obtain a polymeric absorbent foam material such as a collapsed absorbent foam material expanding upon contact with aqueous liquids.

Absorbent foams formed by polymerizing the emulsions prepared by the process of the present invention have an average cell size of about 5 to 100 microns and are particularly suitable for absorbing body fluids.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in greater detail by the following detailed description and accompanying drawings.

Description of the picture

Fig. 1 is a photomicrograph of the extracellular spaces of a polymerized HIPE emulsion of the type produced by the method of the invention.

Fig. 2 is a schematic flow diagram showing arrangements of apparatus and devices that can be used to carry out the method of the invention.

The emulsions prepared by the process of the invention are water-in-oil emulsions with a relatively high ratio of aqueous phase to oil phase. As mentioned, emulsions of this type having a relatively high aqueous phase to oil phase ratio are known in the art as High Intemal Phase Emulsion HIPE. HIPE emulsions having the aqueous and oil phase characteristics of the present invention are suitable for polymerization (and dewatering) to foam materials which are particularly suitable for absorbents of aqueous body fluids.

Each of the essential steps of preparing HIPE emulsions of this type in a continuous manner is described in detail below:

A) Ensure the oil phase supply

The particular oil phase incorporated into the HIPE emulsions prepared by the process of the invention consists of monomers that polymerize to rigid foam structures when the emulsions made from such an oil phase are optionally subjected to polymerization conditions. The monomers especially used in this oil phase include the major monomer component, the comonomer component and the crosslinker. The choice of the appropriate types and amounts of monofunctional main monomer or monomers and comonomers or comonomers and polyfunctional crosslinking agent or agents may be important to realize HIPE-based absorbent foams having the desired combination of 40 properties that give such foams suitability for use as aqueous body fluid absorbents. .

The major monofunctional monomer component in the oil phase used to prepare the HIPE emulsions is one or more monomers which tend to impart similar properties to the possible foam structure of the glass 45. These monomers are hereinafter referred to as vitreous monomers and for the purposes of the present invention are defined as monomeric materials which form homopolymers of high molecular weight (greater than 6000) with a glass transition temperature Tg of about 40 ° C. A preferred type of monofunctional glassy monomer is styrene-based monomer, and styrene itself is the most preferred monomer of this kind. 50 substituted, for example monosubstituted styrene, such as paramethylstyrene, may also be used. The monofunctional glassy monomer component will normally consist of about 3 to 41% by weight, more preferably 7 to 40%, of the oil phase used to form the HIPE emulsions.

In addition to the main vitreous monomer material, the monofunctional comonomer component is also present in the oil phase used in the instant HIPE emulsion preparation process. Such a monofunctional comonomer component consists of one or more comonomers which tend to impart rubbery properties to foams, possibly resulting from the polymerization of such prepared emulsions. These comonomers are hereinafter referred to as rubbery comonomers and for the purposes of the invention are defined as monomeric materials which form homopolymers of high molecular weight (greater than 6000) with a glass transition temperature Tg of about 40 ° C or less. Monofunctional rubbery comonomers of this type include, for example, alkyl acrylates, alkyl methacrylates, allylacrylates, substituted butadienes, vinilidene halides, and mixtures of such comonomers and comonomer types. Preferred comonomers are butyl acrylate, 2-ethylhexyl acrylate, butadiene, isoprene and mixtures of these comonomers. Most preferred are butyl acrylate and 2-ethylhexyl acrylate. The monofunctional rubbery comonomer component normally consists of about 27-73% by weight, more preferably about 27-66%, of the oil phase used to form the HIPE emulsions.

In the oil phase used to form the emulsions, both the monofunctional glassy monomer (s) and the monofunctional rubbery comonomer (s) must be present in the HIPE within the concentration range indicated. In addition, the molar ratio of the monofunctional glassy monomer to the monofunctional rubbery comonomer in the oil phase is usually about 1: 25 to 1.5: 1, more preferably about 1: 9 to 1.5: 1.

Since the polymer chains formed by the glassy monomer (s) and the rubbery comonomer (s) are to be crosslinked when the prepared emulsions are subsequently polymerized, the oil phase must also contain a polyfunctional crosslinking agent. As with monofunctional monomers and comonomers, the choice of individual type and amount of crosslinking agent can be very important for the eventual realization of a HIPE emulsion which is polymerizable to foams with the desired combination of structural, mechanical and liquid absorption properties.

Depending on the type and amount of monofunctional monomers and comonomers used, and further on the desired properties of any polymeric foams optionally implemented, the polyfunctional crosslinking agent for use in the oil phase may be selected from a variety of polyfunctional, preferably diffusing monomers. Thus, the crosslinking agent may be a divinyl aromatic material such as divinylbenzene, divinyltoluene or diallyl phthalate. Alternatively, divinyl aliphatic crosslinkers such as polyacrylic acid esters can be used. Divinylbenzene has been found to be the preferred crosslinking agent to prepare the most acceptable foaming HIPE emulsions.

It is generally used in the oil phase used to prepare the crosslinking agent emulsion of any type in an amount of about 8 to 40% by weight, more preferably about 10 to 25%. The amount of crosslinking agents in such a range will generally provide a molar crosslinker concentration of about 5 to about 60 mole percent based on the total amount of monomers present in the oil phase.

The major part of the oil phase used to prepare the HIPE emulsions consists of said monomers, comonomers and crosslinking agents, which optionally form polymeric foam absorbents. It is therefore desirable that these monomers, comonomers and cross-linking agents be substantially water-insoluble and are primarily soluble in the oil phase and not in the aqueous phase of the emulsions. The use of such substantially water-insoluble monomeric materials ensures that stable HIPE emulsions of adequate characteristics are obtained.

However, it is preferred that the monomers, comonomers and cross-linking agents used to form the foam precursor emulsions are of the type that the polymer is non-toxic and sufficiently chemically stable when foam is formed. Such monomers, comonomers and crosslinking agents should therefore be non-toxic or exhibit low toxicity at very low residual levels.

These are possible concentrations during the processing of the foam after polymerization and / or in use.

Another essential component of the oil phase used to form the HIPE emulsions of the present invention is an emulsifier to form stable HIPE emulsions. Such emulsifiers are oil-soluble emulsifiers used to form the emulsion. The emulsifiers used may be nonionic, cationic, anionic or amphoteric if the emulsifier or emulsifier mixture forms stable HIPE emulsions. Suitable emulsifiers that can be used to provide an emulsifying component with suitable properties are sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene acids (POE), and fatty acid esters. Particularly preferred are sorbitan fatty acid esters such as sorbitan monolaurate (SPAN ^R 20), sorbitan monooleate (SPAN ^r 80) and mixtures of trioleate (SPAN ^R 85) and sorbitan monooleate (SPAN ^R 80). One such particularly preferred combination is a combination of sorbitan monooleate and sorbitan trioleate in a weight ratio greater than or equal to 3: 1, more preferably 4: 1. Another functioning emulsifier is TRIODAN ^R 20, which is a commercially available polyglycerol ester from Grindsted and EMSORB 2502, which is sorbitan sequioleate from Henkel.

The emulsifying component generally comprises about 2 to 33% by weight of the oil phase used to form HIPE emulsions, which are then used to prepare polymeric absorbent foams. More preferably, the emulsifying component constitutes about 4 to 25% by weight of the oil phase.

In addition to the monomers and emulsifiers described above, the oil phase used to form the polymerizable HIPE emulsions may also contain additional optional components. One such optional component of the oil phase may be an oil-soluble polymerization initiator of the general type described hereinafter. Another possible oil phase component may be a substantially water-insoluble solvent or carrier of the oil phase monomer components, crosslinking agent and / or emulsifier. However, a solvent or carrier of this type must not be able to dissolve optionally polymerized monomers. The use of such solvents is not suitable, but when such a solvent or carrier is used, it will generally not comprise more than about 10% by weight of the oil phase.

The oily phase as described above may itself be prepared by any suitable method by combining the necessary and any components by conventional techniques. Such a combination of components may be carried out either continuously or batchwise in any order of compounding. The oil phase thus prepared is generally formed and stored in a reservoir from which the oil phase can be introduced into the feed at any desired flow rate, as will be described hereinafter.

B) Provision of water phase supply

As indicated, the oil phase described above is a continuous external phase in HIPE emulsions for absorbent foam polymerization. The discontinuous internal phase of such polymerizable HIPE emulsions is the aqueous phase, which is generally an aqueous solution containing one or more dissolved components. Similar to the oil phase, the aqueous phase used to form the HIPE emulsions is supplied to the process in a separate feed.

One necessary dissolved component of the aqueous phase is a water-soluble electrolyte. The dissolved electrolyte in the aqueous phase used to form the HIPE emulsions serves to minimize the tendency of the monomers and crosslinking agents that are primarily oil soluble to also dissolve in the aqueous phase. This, in turn, can minimize the extent to which cell windows are filled with polymeric material at the oil / water interface formed by the water phase bubbles when the emulsion is subsequently polymerized. The presence of an electrolyte and the resulting ionic strength of the aqueous phase can therefore determine whether and to what extent the resulting open cell polymer foams may be possible.

Any electrolyte with ionic substances imparting ionic strength to the aqueous phase can be used. Preferred electrolytes are monovalent, divalent or trivalent inorganic salts such as

Water soluble halides (such as chlorides), alkali metal and rare earth metal nitrates and sulfates. Examples are sodium chloride, calcium chloride, sodium sulfate and magnesium sulfate.

The most preferred electrolyte for use in the aqueous phase is calcium chloride.

Generally, the electrolyte in the aqueous phase used herein to form the HIPE emulsions is at a concentration of about 0.2 to about 40% by weight of the aqueous phase. More preferably, the electrolyte content is about 0.5 to 20% by weight of the aqueous phase.

In addition to the necessary aqueous and oil phases described above, the HIPE emulsions produced by the process according to the invention generally also contain a polymerization initiator. Such an initiator component is generally added to the aqueous phase to form HIPE emulsions and may be any conventional water-soluble radical. Materials of this type include, for example, peroxygen compounds such as soda, potash and ammonium persulfate, capryl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxides, tertiary butyldiperoxy phthalate, tertiary butyl perbenzoate, sodium peroxyacetate and sodium percarbonate 15. Conventional redox indicator systems may also be used. Such systems are formed by combining the foregoing peroxygen compounds with reducing agents such as sodium bisulfite, L-ascorbic acid or ferrous salts.

The initiator may comprise up to about 5 mole percent based on the total mole fraction of the 20 polymerizable monomers contained in the oil phase. More preferably, the initiator is approximately

0.001 to 0.5 mol, based on the total molar proportion of polymerizable monomers (i.e., monomers, comonomers, crosslinkers) in the oil phase. When used in the aqueous phase, the concentrations of such initiators may be adjusted by adding the initiator to the aqueous phase in an amount of about 0.02 to 0.4% by weight, more preferably about 0.1 to 0.2% of the aqueous phase.

As with the oil phase, the aqueous phase containing the necessary and arbitrary components described above may itself be prepared by combining these components in a conventional manner. Thus, the aqueous phase can be prepared either continuously or in batches while maintaining the appropriate order of addition of the aqueous phase components. Similar to the oil phase, the aqueous phase is prepared and stored in a separate feed tank provided with means for supplying the liquid phase water feed from the tank at any desired flow rate.

C) Initial introduction of oil and water phase feeds into the dynamic mixing zone

Initially the feeds of the above-described liquid oil and water phases are combined by simultaneously introducing the feeds of the two liquid phases into the dynamic mixing zone. The dynamic mixing zone and the mixing emulsion imparted to the liquid phase contents are described in more detail below.

During this initial mixing of the oil and water phase feeds, the flow rates of the feeds are adjusted so that the weight ratio of the water phase to the oil phase introduced into the dynamic mixing zone is considerably lower than in any HIPE emulsions that may be realized. In particular, the flow rates of the liquid oil and aqueous phase feeds are adjusted such that the water to oil weight ratio at this initial stage is about 2: 1 to 10: 1, more preferably about 2.5: 1 to 5: 1.

The purpose of combining the oil and water phase feeds at these relatively low water to oil ratios is to allow at least a certain amount of water-in-oil emulsion to be formed in the dynamic mixing zone that is relatively stable and does not disintegrate readily under the conditions of the dynamic mixing zone.

The actual flow rates of the oil and water phase liquid feeds during this initial introduction into the dynamic mixing zone vary depending on the desired type of emulsion preparation process. In a pilot plant preparation, the oil phase flow rate at this initial initial stage may be about 0.02 to 0.2 liters per minute and the aqueous phase flow rate may be about 0.04 to 2.0 liters per minute. It can be flow-through in industrial operation

196 The oil phase velocity at this initial initial stage is approximately 10 to 25 liters per minute and the water phase flow rate can be approximately 20 to 250 liters per minute.

At the beginning of the process, the dynamic mixing zone is filled with a liquid oil and water phase before mixing is started. During this filling stage, gas is removed from the dynamic mixing zone. Before mixing begins, the liquid in the dynamic mixing zone is formed by two separate phases of oil and water. Once the dynamic mixing zone is filled, stirring is commenced, as described in more detail below, and emulsion formation begins in the dynamic mixing zone. At this point, the flow rates of the aqueous and oil phases should be adjusted to the above range to provide a relatively low water to oil ratio by weight as described above.

D) Initial emulsion formation in the dynamic mixing zone

As mentioned, the oil and water phase feeds are initially combined by simultaneously feeding them to the dynamic mixing zone. For the purposes of the present invention, the dynamic mixing zone comprises a liquid container provided with means for imparting shear mixing to the liquid contents of the container. Such shear mixing means must be suitable to provide mixing or mixing beyond mixing resulting from the mere flow of material through the vessel.

The mixing means used as an element in the dynamic mixing zone may be any suitable device that imparts the necessary amount of shear mixing to the liquid content in the dynamic mixing zone. A suitable type of mixing device is a pin rotor, consisting of a cylindrical shaft from which a series of radially arranged cylindrical pins protrude. The number of pins, their dimensions and the arrangement on the agitator shaft may vary within wide limits, depending on the amount of shear mixing the agitator is to impart to the content in the dynamic mixing zone. As will be discussed in more detail below with reference to the drawing, a pin type stirrer of this type may be housed in a generally cylindrical mixing vessel serving as a dynamic mixing zone. The agitator shaft is mounted generally parallel to the direction of fluid flow through the cylindrical dynamic mixing zone. The shear mixing is achieved by rotating the agitator shaft at a speed that imparts the necessary degree of shear mixing to the fluid material passing through the dynamic mixing zone.

The shear mixing provided to the liquid content that has been introduced into the dynamic mixing zone is such that at least a portion of the dynamic mixing zone content is brought into a water-in-oil emulsion state with a water to oil ratio in the above range. Typically, the stirrer speed at this stage is about 1000 to 7000 / s, preferably about 1500 to 3000 / s. The degree of shear mixing need not be constant, but may vary over time required to form such an emulsion. As noted, not all of the aqueous and oil phase material introduced into the dynamic mixing zone at this stage need to be brought into the water-in-oil emulsion state if at least a portion of the emulsion of this type (i.e. an emulsion consisting at least about 90% by weight of liquid) flow from the dynamic mixing zone) creates and flows through the dynamic mixing zone.

Once the mixing has started, it is important that the flow rates of the aqueous and oil phases are sustained and non-pulsating. This is because sudden, rapid changes in these flow rates can cause the emulsion already formed in the dynamic mixing zone to break down. Likewise, changes in the flow rates of the aqueous and / or oil phase should be sufficiently rapid to avoid significant separation of the emulsion already formed in the dynamic mixing zone into the non-emulsified oil and water phases.

E) HIPE formation in the dynamic mixing zone

After the water-in-oil emulsion has been formed with a relatively low water-to-oil ratio in the dynamic mixing zone by selecting suitable flow rates and shear mixing conditions as described above, measures are taken to convert the resulting emulsion together with other

The unmixed fractions in the dynamic mixing zone on the emulsion with a high internal fraction of the aqueous phase, i.e. HIPE. This is achieved by varying the relative flow rates of the aqueous and oil phase streams fed to the dynamic mixing zone. Such an increase in the water to oil ratio in the feed phases can be achieved by increasing the water flow rate or reducing the oil flow rate, or a combination of both. The water to oil ratios thus realized by adjusting the flow rates of the aqueous and / or oil phase are generally 12: 1 to 100: 1, more preferably from about 20: 1 to 70: 1, most preferably about 25: 1 to 50: 1.

Adjusting the flow rates of the oil and water phases to increase the ratio of water to oil phases of the liquid material impregnated into the dynamic mixing zone can be started immediately after the initial slurry formation in the dynamic mixing zone. This generally occurs soon after mixing is started in the dynamic mixing zone. The time interval to increase the water-to-oil ratio to the final desired higher ratio depends on the size of the process and the amount of any water-to-oil ratio to be achieved. Often the adjustment of the increased water to oil ratio takes about 1 to 5 minutes.

When varying the relative flow rates of the aqueous and oil phases to achieve the final desired relative water to oil ratios for the preparation of HIPE emulsions, care should be taken to progress towards these desirable ratios. As already mentioned, sudden or sudden changes in the flow rates of the aqueous phase and / or the oil phase may cause the emulsion to break up in the dynamic mixing zone before or soon after appropriate HIPE emulsions can be formed. The actual ratio of increasing the ratio of water to oil in the feeds fed to the dynamic mixing zone depends on the individual components of the emulsion being prepared as well as on the scale of the process. For a given HIPE formulation and process type, emulsion stability can be controlled by simply monitoring the nature of the process effluent to ensure that it consists of at least a certain amount of material (e.g. at least 90% of the total effluent) substantially in the form of an HIPE emulsion.

The conditions within the dynamic mixing zone (and ultimately the polymerized absorbent foam formed therefrom) may also change the nature of the HIPE emulsion prepared by the process of the invention. One variable in the dynamic mixing zone that may have an impact on the nature of the HIPE emulsion produced is the temperature of the emulsion components in the dynamic mixing zone. Generally, the emulsified content in the dynamic mixing zone should have a steady temperature of about 25 to 70 ° C, more preferably about 35 to 65 ° C during HIPE formation.

Another variable of the conditions in the dynamic mixing zone is the amount of shear mixing of the allocated content in the dynamic mixing zone both during and after the adjustment of the water phase to oil phase ratio to form HIPE emulsions. The degree of shear mixing imparted to the emulsified material in the dynamic mixing zone has a direct impact on the size of the cells that make up the absorbent foam material, if any. For a given combination of emulsion component types and ratios and for a combination of flow rates of streams fed into the dynamic mixing zone, a greater degree of shear mixing imparted to the liquid content in the dynamic mixing zone tends to reduce cell size in the foam absorbent material made from the HIPE emulsions of the invention .

Foam cells, and in particular cells formed by polymerizing a monomer-containing oil phase that surrounds the monomer-free water phase bubbles, are generally substantially spherical in shape. The size or diameter of such substantially spherical cells is therefore a commonly used parameter for characterizing foams in general, as well as characterizing foams of an absorbent type prepared from HIPE emulsions produced by the method of the invention. Since the cells in a given polymeric foam sample do not necessarily have approximately the same size, the mean cell size, i.e. the mean cell diameter, is often specified.

-10GB 281902 B6

A number of techniques are used to determine the mean cell size. These include mercury porosimetry methods well known in the art. The most useful technique for determining the cell size in foams, however, is a simple photographic measurement of the foam sample. For example, Fig. 1 is a photomicrograph of a fracture surface of a typical foam absorbent structure prepared from the HIPE emulsions produced according to the invention. The microscope is accompanied by a scale representing 10 micrometers. Such a scale can be used to determine the mean cell size by analyzing the image. Image analysis micrograph of foam samples is indeed a commonly used analytical method that can be used to determine the mean cell size of foam structures. Such a technique is described in more detail in U.S. Patent 4,788,225, Edwards et al., Issued November 29, 1988.

it

For the purpose of the present invention, medium cell sizes in foams can be used by polymerizing the HIPE emulsions prepared by the method of the invention to quantify the degree of shear mixing imparted to the emulsified content in the dynamic mixing zone during the instant process. In particular, when the flow rates of the aqueous and oil phases have been adjusted to provide the required water-in-oil ratio for HIPE 15, the emulsified content in the dynamic mixing zone should be subjected to shear mixing sufficient to eventually form an HIPE emulsion which cells of about 5 to 100 microns. More preferably, stirring is capable of realizing a mean cell size in the subsequently formed foam of about 10 to 90 microns. This is generally a shear mixing corresponding to a rotation speed of about 1000 to 7000 per second, more preferably from about 1500 to 3000 per second.

Regarding the shear mixing used to initially introduce the aqueous and oil phases into the dynamic mixing zone, the shear mixing to provide HIPE emulsions may not be constant throughout the process. For example, the agitator speed can be increased or decreased in the HIPE 25 preparation process as required or required to provide foam-forming emulsions with a particular desired mean cell size as specified above.

F) Transfer of effluent from the dynamic mixing zone to the static mixing zone

In the method of the invention, the liquid content containing the emulsion in the dynamic mixing zone is continuously withdrawn from the dynamic mixing zone and introduced into the static mixing zone where it is subjected to further mixing and mixing. However, the nature of the dynamic mixing zone effluent will change with time as the process proceeds from initial start to initial emulsion formation in the dynamic mixing zone to the HIPE emulsion in the dynamic mixing zone while increasing the water to oil ratio. During the start of the process, the effluent from the dynamic mixing zone may contain little or no emulsified material. Then, when the emulsion begins to form in the dynamic mixing zone, the effluent therefrom consists of a water in oil emulsion with a relatively low water to oil ratio, together with an excess of oil and water phases that have not passed into the emulsion. Finally, when the ratio of the aqueous to oil feed stream in the dynamic mixing zone 40 has been increased, the effluent from the dynamic mixing zone consists of HIPE along with a relatively small amount of oil and water phases that have not passed into the HIPE.

Once steady-state operation is achieved, the flow rate of the outflow from the dynamic mixing zone that becomes the feed current to the static mixing zone is equal to the sum of the flow rates of the water and oil phases introduced into the dynamic mixing zone. After properly adjusting the flow rates of the aqueous and oil phases to ensure the formation of the desired HIPE emulsion, the flow rate of the dynamic mixing zone in a commercial production range is generally about 35 to 800 liters per minute. On a pilot scale, the rate of discharge from the dynamic mixing zone is about 0.8 to 9.0 liters per minute.

The effluent continuously withdrawn from the dynamic mixing zone is continuously introduced into the static mixing zone for further processing. The static mixing zone constitutes resistance to the flow of fluid material through the process operations and thus exerts back pressure on the liquid content of the dynamic mixing zone. However, the primary purpose of the static mixing zone in this process is to subject it

The emulsified material from the dynamic mixing zone is additionally mixed and mixed to complete formation of the desired stable HIPE emulsion.

For the purpose of the present invention, the static mixing zone may consist of any suitable liquid material container 5, which is adapted to impart mixing or mixing to such materials as the liquid materials flowing through the container. A typical static mixer is a spiral mixer, which may be formed by an oven having an internal arrangement to form a series of spirals that change direction after every 180 ° of the spiral thread. Each 180 ° thread of the internal screw arrangement is called an arm. Generally, a static mixer with 12 to 32 arms intersecting at 90 ° is suitable for the process.

In the static mixing zone, the shear forces placed in the liquid material placed therein are simply caused by the internal arrangement of the static mixing device on the liquid flowing therethrough. Typically, the shear is imparted to the liquid contents in the static mixing zone at a speed of approximately

100 to 7000 per second, more preferably about 500 to 3000 per second.

In the static mixing zone, all the aqueous and oil phase material that has not been incorporated into the emulsion in the dynamic mixing zone upon reaching the HIPE water to oil ratio is necessarily formed into a stable HIPE emulsion. Typically, such an emulsion ΗΊΡΕ has an aqueous to oil phase ratio of approximately

12: 1 to 100: 1, more preferably about 20: 1 to 70: 1. Such emulsions are stable in that they do not substantially separate into their aqueous and oil phases for at least the time required to allow polymerization of monomeric contents in their oil. stage.

G) Polymerizable HIPE emulsions from the static mixing zone

The emulsified material may be continuously withdrawn from the static mixing zone at a rate close to the sum of the flow rates of the water and oil phase feeds to the dynamic mixing zone. After increasing the water-to-oil ratio of the feed materials to the desired level for HIPE and after reaching steady-state conditions, the effluent from the static mixing zone is formed by a substantially stable 30 HIPE emulsion suitable for further processing into absorbent foam material.

Stable HIPE emulsions of the above composition can be converted to useful foam materials by subjecting these HIPE emulsions to suitable polymerization and dewatering. This results in polymerization of the monomeric materials contained in the oil phase of the stable HIPE 35 water-in-oil emulsions to a solid polymeric foam-like structure. The polymeric foam structures formed by the polymerization of the respective HIPE emulsions obtained by this process are relatively open cell. That is, the individual cells of the resulting foam are usually not completely isolated from each other by another polymeric material filling the cell walls. Cells in such substantially open cell foam structures have intercellular spaces or windows 40 that are large enough to allow easy flow in the foam structure from one cell to another. This makes such foams particularly suitable for liquid absorbents.

In substantially open cell structures of the type that can be prepared from the HIPE emulsions produced by the method of the invention, the foam is generally net-like in nature, wherein individual cells 45 are defined by a plurality of interconnected, three-dimensional branched tissues. The strands of polymeric material that treat the branched tissues of the open-cell foam structure can be defined as struts. Open cell foams with a typical strut-like structure are shown by way of example in Fig. 1.

The polymerization of the HIPE emulsions to form absorbent foams can be accomplished by placing the HIPE emulsions in a suitable polymerization container and subjecting the emulsion to curing conditions. Such curing conditions may be maintained at a temperature of about 55 to 90 ° C for about 4 to 24 hours. The foamed materials so formed are usually also further processed to render them suitable for liquid absorbents. Subsequent processing may include:

- 12GB 281902 B6 for example a) washing the foam structure to remove residual aqueous phase from the foam cells, b) treating the foam structure with a hydrophilizing agent to render the inner surfaces of the foam suitable for absorbing hydrophilic liquids such as aqueous body fluids, c) dewatering by compression and / or heating to expel residual water to such an extent that such foams are effective to absorb aqueous body fluids; and / or d) cutting or otherwise shaping to obtain a suitable shape for incorporation into absorbent articles. Absorbent foam materials that can be prepared from the HIPE emulsions produced by the method of the invention are described in more detail in US Patent Application No. 07 743839, DesMarais, Stone, Thompson, Young, LaVon, and Dyer (P&G No. 4451), Aug. 12, 1991.

Equipment

The process for the continuous preparation of the HIPE emulsions of the present invention can be carried out in a conventional liquid processing apparatus. A typical arrangement of such a device is shown in Fig. 2 by a schematic flow diagram.

As can be seen from FIG. 2, an apparatus suitable for carrying out the process according to the invention may consist of an oil phase container 1 and an aqueous phase container 2. The liquid oil phase is passed through the oil phase feed line 3 and the oil phase feeder 5, the oil phase heat exchanger 7 and the oil phase metering tube 9 into the dynamic mixer vessel 11. Similarly, the aqueous phase liquid material is fed through the aqueous phase feed line 4 and the aqueous phase feeder 6, the aqueous phase heat exchanger 8 and the aqueous phase metering tube 10 to the vessel 11 of the dynamic mixer.

The dynamic mixer vessel 11 is provided with an exhaust 12. The ventilation of air from the dynamic mixer vessel 11 is controlled by the exhaust valve 13. It is ventilated during filling of the vessel and may be performed as needed to maintain a humid environment in the dynamic mixer vessel 11. The oil phase metering tube 9 and the aqueous phase metering tube 10 serve to provide a steady stream of oil and water phases to the mixer and are to be sized to maintain a pressure difference between the feed line and the dynamic mixer vessel 11 of about 13.8 kPa at a deliberate flow rate.

The dynamic mixer vessel 11 is also provided with a pin mixer 14. The pin mixer 14 consists of a shaft 15 supporting a row, for example 16 or 17 arms of cylindrical mixing pins 16 projecting radially from the agitator shaft. These arms of the cylindrical mixing pins 16 are in four rows along the stirrer shaft and are spaced 90 ° along the periphery of the shaft 15. The rows of mixing pins 16 are offset over the length of the stirrer shaft 15 so that the arms perpendicular to each other do not lie in in the same radial plane passing through the shaft axis 15. The pin mixer 14 serves to impart shear mixing to the liquid content in the dynamic mixer vessel 11 to form emulsified material in the dynamic mixer vessel 11. Such emulsified material is withdrawn from the dynamic mixer vessel 11 through the dynamic mixer outlet line 17 and is fed to the static mixer vessel 18.

The emulsified liquid material is subjected to further agitation or mixing in the static mixer vessel 18 and is withdrawn from the static mixer vessel 18 through the static mixer discharge conduit 19. When such effluent is in the form of a stable HIPE emulsion, it may be discharged through the outlet conduit 19 and the outlet conduit valve 20 to a suitable polymerization tank 21. The stable HIPE in the polymerization tank 21 may be subjected to polymerization conditions to produce the desired absorbent foam material.

The following examples illustrate the preparation of water-in-oil emulsions with a high internal fraction of the aqueous phase and their subsequent polymerization and dewatering to absorbent foam. The processes described are generally carried out on a pilot scale using apparatus substantially similar to those just described with reference to FIG. 2.

- 13GB 281902 B6

DETAILED DESCRIPTION OF THE INVENTION

Example 1

320 g of calcium chloride and 48 g of potassium persulfate are dissolved in 32 liters of distilled water. This provides the water phase supply for the subsequent HIPE emulsion formation process.

450 g of sorbitan monooleate (as SPAN ^R 80) and 150 g of sorbitan trioleate (as SPAN ^R 85) are added to the monomer mixtures consisting of 420 g of styrene, 660 g of divinylbenzene and 1920 g of 2-ethylhexyl acrylate. After mixing, this provides an oil phase feed for the subsequent HIPE emulsion formation process.

At liquid temperatures of 55 ° C to 65 ° C, separate streams of oil and water phases are fed to the dynamic mixing apparatus. Thorough mixing of the combined streams in the dynamic mixing apparatus is achieved with a pin mixer. In this pilot plant, the respective pin mixer consists of a cylindrical shaft of approximately 180 mm in length and approximately 19 mm in diameter. The shaft carries two rows of 17 and two rows of 16 cylindrical pins with a diameter of 5 mm, projecting radially outwardly from the central axis of the shaft to a length of 10 mm. The four rows are spaced 90 ° along the perimeter of the stirrer shaft, the rows perpendicular to each other and offset over the length of the shaft as shown in the drawing. The pin mixer is housed in a cylindrical housing which forms a dynamic mixing device and the stirrer pins have a clearance of 0.8 mm from the walls of the cylindrical housing. The stirrer is rotated at 900 rpm.

A downstream dynamic mixer is mounted with a static mission (203.2 mm long, 6.35 mm external diameter, and 4.826 mm internal diameter) with the internal spiral arrangement described above to create a back pressure in the dynamic mixer. This helps keep the dynamic mixer with the cylindrical housing and the pin mixer full of liquid. The static mixer also helps to ensure adequate and complete formation of the HIPE emulsion from the oil and aqueous phases.

Optionally, an emulsion with a desired aqueous to oil phase ratio is eventually obtained. First, the flow rates are set so that 3 parts by weight of the aqueous phase and 1 part of the oil phase enter the dynamic pin mixer. The ratio of aqueous phase to oil phase is increased to 12-13 parts of aqueous phase to 1 part of oil phase entering the dynamic mixer at a rate of 15 ml / sec over 5 minutes. Gradually, the oil flow rate decreases so that the weight ratio of the aqueous phase to the oil phase approaches 25: 1. At this stage, the viscosity of the emulsion exiting the static mixer decreases. (At visual observation, the whitish mixture appears to be more translucent at this point).

Then the flow rate of the oil phase is further reduced until the desired ratio of water phase to oil phase of 30 to 33: 1 is reached. At this stage, the emulsion visually emerges from the opening of the static mixer visually to the consistency of the spreading cream and precipitates to a creamy-like consistency.

At this stage, the emulsion leaving the static mixer is ready for curing. The emulsion is filled into a square polyethylene mold of length 380 mm, width 250 mm and depth 220 mm. The emulsion is filled into such molds until each mold contains approximately 20,000 ml of the emulsion to cure.

For curing, the emulsion-containing molds are placed in a curing oven at 60 ° C for about 16 hours. After curing, the resulting solid polymeric foam material contains up to 98% water and is soft and soft to the touch.

At this stage, the material may be subjected to further processing to render it suitable for use as an absorbent for aqueous body fluids. Such further processing may be washing

- 14GB 281902 B6 foam to remove residual water and oil phase components, treat the foam with hydrophilizing agents to achieve hydrophilic inner surfaces, and drainage to provide relatively dry foam material.

When the material thus prepared is dried and subjected to photomicrographic analysis as described, it can be said that the material has a mean cell size of about 40 microns.

Example 2

Another HIPE emulsion (and the polymeric foam material produced therefrom) was prepared generally in the same manner as in Example 1. In this example, the emulsion preparation and polymerization process were carried out as in Example 1, but with the following differences in materials, concentrations and conditions :

1) 480 g of SPAN ^R 80 and 120 g of Span ^R 85 are used as emulsifiers in the oil phase.

2) A static mixer 356 mm long with a diameter of 95 mm is downstream of the dynamic mixer.

3) The pellet mixer speed in the dynamic mixer is 850 rpm.

4) The final weight ratio of aqueous to oil phase of the HIPE emulsion produced is 31: 1.

5) A curing temperature of 66 ° C is used.

After drying as in Example 1, the foam in Example 2 is subjected to photomicrographic analysis to determine that the material has an average cell size of 37 microns.

Example 3

This example illustrates the preparation of another type of HIPE emulsion (and the polymeric foam material produced therefrom) within the scope of the invention.

Dissolve 36.32 kg of calcium chloride and 568 g of potassium persulfate in 378 liters of water. This provides an aqueous phase in a continuous process to form the HIPE.

960 g of sorbitan monolaurate (as SPAN ^R 20) are added to the monomer mixture consisting of 1600 g of styrene, 1600 g of 55% technical divinylbenzene and 4800 g of 2-ethylhexyl acrylate. After mixing, the mixture of materials was allowed to stand overnight. The supernatant is withdrawn and used as an oil phase in a continuous HIPE emulsion formation process. (About 75 g of solid residue is discarded).

At an aqueous phase temperature of 48-50 ° C and an oil phase temperature of 22 ° C, separate streams of oil and water phases are introduced into the dynamic mixer. Thorough mixing in the dynamic mixer is achieved with a pin mixer. On this scale, the pin mixer has a cylindrical shaft of about 216 mm and a diameter of 19 mm. The shaft described in Example 1 carries 4 rows of pins, 2 rows of 17 pegs and 2 rows of 16 pegs with a diameter of 5 mm, which project outwardly from the central axis of the shaft to a length of 16 mm. The pin mixer is housed in a cylindrical housing forming a dynamic mixer and the pins have a clearance of 0.8 mm from the walls of the cylindrical housing.

Downstream of the dynamic mixer, a static spiral mixer is built-in to create back pressure in the dynamic mixer and to improve the incorporation of ingredients into the emulsion that may be formed. Such a static mixer is 356 mm long and has an outer diameter of 13 mm. The static mixer is modified by 61 mm shortening from model 070-821 TAH Industries.

The combined mixer is filled with oil and water phases in a ratio of 2 parts water to 1 part oil. The dynamic mixer is vented to allow air to escape until the instrument is completely filled. Speed

The flow rates during filling are 1.127 g / s of the oil phase and 2.19 cm vod / s of the aqueous phase.

Once the machine is filled, mixing is started in a dynamic mixer with a stirrer speed of 1800 rpm. The flow rate of the aqueous phase is then continuously increased up to 35.56 cm ³ / s in a time interval of 130 seconds. The back pressure created by the dynamic and static mixer at this time is 51.75 kPa. The stirrer speed gradually decreases to 1200 rpm over a period of 60 seconds. The back pressure drops to 31.05 kPa. At this point, the stirrer speed is immediately increased to 1800 rpm. The back pressure in the system then remains constant at 31.05 kPa.

The formed emulsion, now emerging from the static mixer, is collected in Rubbermaid Econonmy Cold Food Storage Boxes, Model 3500. These boxes are made of food polyethylene and have a nominal size of 457 x 660 x 229 mm. The actual internal dimensions of the boxes are 381 x 584 x 229 mm. These boxes are precoated with a 20% SPAN ^R 20 solution of the same weight of the xylene-isopropanol solvent mixture. The solvent mixture was allowed to evaporate leaving only SPAN ^R 20. 47 liters of emulsion were filled into each box.

The boxes containing the emulsion are stored at 65 ° C for 18 hours to induce polymerization of the emulsion in the boxes to form a polymeric foam material. Once curing is complete, the moist foam material is removed from the curing boxes.

The foam material is now subjected to further processing to dewater the foam leaving the residual amount of hydrophilizing agent - calcium chloride - in the foam structure. After such treatment, the foam material has a residual water content of about 5-7% by weight of polymerized material (including hydration water) and contains residual sorbitan monolaurate in an amount of about 11% and hydrated calcium chloride in an amount of about 5% (anhydrous base).

Such a foam is of the thin-until-wet type, which means that such a foam shrinks to a relatively smaller caliper by dewatering, but again expands in its caliper when it encounters and subsequently inhibits aqueous body fluids. The thin-until-wet foam material prepared according to Example 3 has an average cell size of about 15 microns in its expanded state.

Example 4

This example illustrates the preparation of yet another type of HIPE emulsion (and subsequent formation of a thin-until-wet polymeric foam formed therefrom) according to the invention.

Dissolve 36.32 kg of calcium chloride and 568 g of potassium persulfate in 378 liters of water. This produces the aqueous phase used in the following process to form the HIPE.

480 g sorbitan monolaurate (as SPAN ^R 20) and a mixture of sorbitan monolaurate and sorbitan monopalmitate (240 g SPAN ^R 20 and 240 g SPAN ^R ) are added to a monomer mixture consisting of 1600 g styrene, 1600 g 55% technical divinylbenzene and 4800 g 2-ethylhexyl acrylate 40) to facilitate dissolution of SPAN ^R 40. After mixing, this oil phase is allowed to stand overnight. The supernatant is withdrawn and used in the following process. (About 75 g of solid residue is discarded).

At an aqueous phase temperature of 48-50 ° C and an oil phase temperature of 22 ° C, separate streams of oil and water phases are introduced into the dynamic mixer. Thorough mixing in the dynamic mixer is achieved with a pin mixer. On this scale, the pin mixer has a cylindrical shaft of about 216 mm and a diameter of 19 mm. The shaft carries 4 rows of pins, 2 rows of 17 pins and 2 rows of 16 pins with a diameter of 5 mm, which protrude outside the central axis of the shaft up to 16 mm. The pin mixer is housed in a cylindrical housing forming a dynamic mixer a

- 16GB 281902 B6 the pins have a clearance of 0.8 mm from the walls of the cylindrical housing.

A downstream dynamic mixer is a static spiral mixer (356 mm long and 13 mm outer diameter, adjusted by 61 mm shortening from 070-821 TAH Industries) to create back pressure in the dynamic mixer and to improve the incorporation of components into the emulsion that will eventually be created.

The combined mixer is filled with oil and water phases in a ratio of 2 parts water and 1 part oil while venting to escape air until the unit is fully filled. The flow rates during filling are 1.5 g / s oil phase and 3.0 cm ³ / s water phase.

Once the machine is filled, mixing is started in a dynamic mixer with a stirrer speed of 1800 rpm. The flow rate of the water phase is then continuously increased up to 43.50 cm ³ / s with a time interval of 40 seconds. The back pressure created by the dynamic and static mixer at this time is 58.65 kPa. The stirrer speed is gradually reduced to 1400 rpm over a period of 60 seconds. The back pressure drops to 31.05 kPa. At this point, the stirrer speed is immediately increased to 1800 rpm. The back pressure in the system then remains constant at 31.05 kPa.

The formed emulsion, now emerging from the static mixer, is collected in Rubbermaid Econonmy Cold Food Storage Boxes, Model 3500, with nominal dimensions of 457 x 660 x 229 mm and with actual internal dimensions of 381 x 584 x 229 mm. The molds are pre-coated with a solution of 20% SPAN ^R 20 in xylene (which is also allowed to evaporate and only the clear supernatant is used). The molds are preheated, which causes the xylene to evaporate, leaving only SPAN ^R 20. 47 liters of emulsion are filled into each mold.

The filled molds are stored at 65 ° C for 18 hours to cure the emulsion. Once curing is complete, the moist foam material is removed from the curing boxes. The foam currently contains about 30-40 times the weight of the polymerized material (30-40x) of the residual aqueous phase containing dissolved emulsifier, electrolyte, and initiator. The foam is divided by a sharp razor blade into strips with a caliper of 0.89 cm. These strips are then compressed in a series of squeezing rollers which gradually reduce the residual aqueous phase of the foam to about six times (6x) the weight of the polymerized material. At this point, the strips are restored with a 1% calcium chloride solution at 60 ° C, squeezing to about 10 times the water phase content.

Foam strips, which now contain about 10 times the substantially 1% calcium chloride solution, are passed through vacuum squeeze rollers. The last roller reduces the calcium chloride solution to about five times (5x) the weight of the polymer. After passing through the last roller, the foam remains compressed on the caliper about 0.2 cm. Then, the foam is dried in a forced air oven at about 60 ° C for about 3 hours. This drying reduces the moisture content to about 5-7% by weight of the polymerized material.

Such a foam is of the thin-until-wet type, which means that such a foam shrinks to a relatively smaller scale by dewatering, but again expands to its extent if it encounters aqueous body fluids and subsequently soaks them. The thin-until-wet foam material prepared according to Example 4 has an average cell size of about 12 microns in its expanded state.

The HIPE emulsions prepared by the continuous process of the invention, which are particularly suitable for subsequent polymerization and dewatering to form thin-until-wet foams, can be realized by selecting some preferred processing parameters. In particular, thin-until-wet HIPE emulsions can be prepared by use

A) an oil phase emulsifier selected from sorbitan monolaurates (e.g. SPAN ^R 20) and a mixture (e.g. 1: 1 to 10: 1 weight ratio) sorbitan monolaurates (e.g. SPAQN ^r 20) and a co-emulsifier selected from polyglycerol esters and sorbitan monopalmitate

- 17EN 281902 B6 (eg SPAN ^r 40), fatty acids,

B) temperatures in the dynamic mixing zone of about 25 ° C to 50 ° C, or even 25 ° C to 60 ° C,

C) shear mixing in a dynamic mixing zone sufficient to optionally form an emulsion

HIPE by subsequent polymerization to provide foam with a mean cell size of about 5 to 30 microns,

D) and in particular a relatively higher ratio of glassy monomer to rubbery comonomer in the oil phase such that, for example, the molar ratio of glassy monomer to rubbery comonomer is about 1: 2 to 1: 1.

Industrial applicability

Process for the continuous preparation of emulsions with a high internal fraction of an aqueous phase, which are suitable for subsequent polymerization to polymeric foam materials which, after dewatering, are useful as absorbents of aqueous body fluids.

Claims (11)

PATENT CLAIMS A process for continuously preparing a water-in-oil emulsion with a high internal fraction of an emulsion phase, suitable for subsequent polymerization and dewatering to form an absorbent foam material, such as a warped but expandable absorbent foam material, characterized in that: A) a liquid oil phase stream comprising by weight (i) from 3 to 41% of at least one water-insoluble styrene-based monomer; iii) having a molar ratio of at least one water-insoluble styrene-based monomer to a monofunctional rubbery comonomer component in the oil phase in the range of 1:25 to 1.5: 1; iv) 8 to 40% water-insoluble crosslinking agent; and (v) from 2 to 33% of an oil-soluble emulsifier component, forming a stable water-in-oil emulsion; and B) an aqueous phase stream consisting of an aqueous solution containing 0.2 to 40% by weight of a water-soluble electrolyte, (C) are simultaneously introduced into the dynamic mixing zone at flow rates at which the initial water to oil phase weight ratio is in the range of 2: 1 to 10: 1; - 18GB 281902 B6 D) in the dynamic mixing zone, the combined streams are subjected to shear agitation at a rate of 1000 to 7000 s * ¹ to form an emulsified mixture and to maintain constant velocities of the oil and aqueous phase streams, then E) the ratio of the aqueous phase to the oil phase fed to the dynamic mixing zone is continuously increased in the range of 12: 1 to 100: 1 at an increasing rate of said ratio maintaining the emulsified nature of the content in the dynamic mixing zone and maintaining this at 25 to 70 ° C whilst continuing to shear the emulsified content in the dynamic mixing zone at a rate of 100 to 7000 s ^-1 and forming an emulsion with a high internal fraction of the emulsion phase, providing subsequent polymerization with a foam having an average cell size of 5 to 100 microns, then F) continuously emulsifies the emulsified content from the dynamic mixing zone and introduces it to the static mixing zone, where it is further subjected to further shear mixing to form a completely stable emulsion with a high internal emulsion phase having a water phase to oil phase weight ratio of 12: 1 to 100: 1 then G) The stable emulsion with a high internal fraction of the emulsion phase continuously withdraws from the static mixing zone and subsequently polymerizes and dewateres to a rigid absorbent foam. Method according to claim 1, characterized in that it is: A) a liquid oil phase stream comprising by weight i) from 7 to 40% of at least one water-insoluble styrene-based monomer, ii) from 27 to 66% of water-insoluble monofunctional rubbery comonomer component, iii) with a molar ratio of styrene-based monomer component to monofunctional rubbery comonomer component in the oil phase 1: 2 to 1: 1; iv) 10 to 25% water insoluble crosslinking agent; and (v) from 4 to 25% of an oil-soluble emulsifier component, forming a stable water-in-oil emulsion; (B) an aqueous phase stream consisting of an aqueous solution containing from 0.5 to 20% by weight of a water-soluble electrolyte; (C) are simultaneously introduced into the dynamic mixing zone at flow rates at which the initial weight ratio of the aqueous phase to the oil phase is in the range of 2.5: 1 to 5: 1; D) the combined streams are subjected to shear mixing in the dynamic mixing zone at a speed of 1500 to 3000 s ^-1 , E) the ratio of the aqueous phase to the oil phase fed to the dynamic mixing zone is continuously increased in the range of 20: 1 to 70: 1 at an increasing rate of said ratio maintaining the emulsified nature of the content in the dynamic mixing zone and maintaining this content at 25 to 65 ° C, preferably 35 to 50 ° C, while continuing to shear the emulsified content in the dynamic mixing zone at a speed of 1500 to 3000 s ^-1 and forming an emulsion with a high internal fraction of the emulsion phase, providing subsequent polymerization foam with an average cell size of 10 to 90 micrometer, and then - 19GB 281902 B6 F) continuously emulsifies the emulsified content from the dynamic mixing zone and introduces it to the static mixing zone, where it is further subjected to further shear mixing to form a completely stable emulsion with a high internal emulsion phase having a weight ratio of water phase to oil phase 20: 1 to 70: 1. 3. The method according to claim 2, wherein it is used (Ii) a water insoluble monofunctional rubbery comonomer component comprising comonomer types selected from the group consisting of butyl acrylate, 2-ethylhexyl acrylate, butadiene, isoprene or a combination of these comonomer types; diallyl phosphate, at least one polyacrylic diacrylate ester, or a combination of such difunctional monomer types, v) an emulsifier component comprising an emulsifier selected from the group consisting of sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene fatty acid esters, and combinations of such emulsifiers; (B) an aqueous solution comprising a water-soluble electrolyte composed of at least one water-soluble alkali metal or alkaline earth metal salt; and E) shear mixing is continued by means of a pin impeller to produce a foam having an average cell size in the range of 5 to 30 microns. A method according to claim 3, characterized in that it is used (Iv) divinylbenzene as a difunctional monomer; and v) an emulsifier component comprising sorbitan monooleate and sorbitan trioleate at a weight ratio of monooleate to trioleate in the range of 2: 1 to 5: 1, or sorbitan monolaurate and a co-emulsifier in a weight ratio of monolaurate to co-emulsifier in the range of 1: 1 to 10: 1; B) calcium chloride as a water-soluble electrolyte. Method according to claim 4, characterized in that it is used B) a water-soluble electrolyte further comprising 0.02-0.4% by weight of a water-soluble free radical polymerization initiator. Method according to claim 5, characterized in that it is used B) a water-soluble electrolyte containing 0.1 to 0.2% by weight of a water-soluble free radical polymerization initiator. Method according to one of the claims 1 to 6, characterized in that the aqueous phase stream is first introduced into the dynamic mixing zone of the pilot plant type at a rate of 0.04 to 2.0 liters / minute and the oil phase stream at a rate of 0.02 to 0.2 liter / minute. Method according to any one of claims 1 to 7, characterized in that the aqueous phase stream is first introduced into the commercial mixing type dynamic mixing zone at a rate of 25 to 250 liters / minute and the oil phase stream at a rate of 10 to 25 liters / minute. -20GB 281902 B6 Method according to one of Claims 1 to 7, characterized in that after increasing the ratio of the aqueous phase to the oil phase, the liquid flowing out of the dynamic mixing zone is withdrawn in the pilot plant at a rate of 0.8 to 2.2 liters / minute. 5 10. The method of claim 8, wherein after increasing the ratio of the aqueous phase to the oil phase, the liquid flowing out of the dynamic mixing zone is withdrawn in a commercial type production plant at a rate of 35 to 800 liters / minute. Process according to any one of claims 1 to 10, characterized in that said stable high internal phase emulsion withdrawn from the static mixing zone is subjected to conditions under which the polymerization of polymerizable monomers, comonomers and crosslinking agents takes place in oil after the subsequent dewatering, a polymeric absorbent foam material such as a collapsed absorbent foam material expands upon contact with aqueous liquids is obtained.